Effects of Foliar Applications of Zinc in the Forms of Free Mineral or Amino Acid Complexed on Qualitative Characteristics of Olive Oil

Abstract

AbstractAn orchard experiment was conducted during two successive years to evaluate the effectiveness of the foliar application of zinc (Zn) in mineral form (ZnSO4) or chelated with various amino acids (AAC) on the oil content, qualitative indices, and fatty acid profile of olive oil. All Zn sources were applied at a rate of 0.2% during two growth stages; at full bloom (FB) and 15 days after FB. The results showed that Zn, regardless of applied sources, accumulated more Zn in leaves and fruits compared to the control. The effectiveness of Zn‐AAC in increasing leaf and fruit Zn concentration was higher than ZnSO4. In both years, an increase in oil content and concentration of phenolic compounds and chlorophyll in the oil was observed when trees were treated with Zn, although these effects were dependent on the Zn sources. In general, the Zn‐AAC treatments, especially Zn‐methionine (Met), was more effective than ZnSO4. Zn‐AAC treatments increased the L* value and b* intensity, while decreasing the a* value of olive oil compared to the control. However, ZnSO4 had a slight or no significant effect on oil color. The oil fatty acid profile was also affected by Zn. The Zn‐Met and Zn‐Glycine (Gly) were more effective than the other Zn sources in increasing monounsaturated fatty acid, specifically oleic acid of oil in both years, respectively. These results could suggest that the application of Zn‐AAC, especially Zn‐Met and Zn‐Gly, can be considered as a new strategy to improve olive oil quality and quantity in Zn‐deficient soils.